The present invention is directed to a railway locomotive traction motor and, in particular, to the friction support bearing by which the traction motor is partially supported on the axle of the railway truck mounting the underside of the locomotive, and, in particular, to a method of customizing the geometry or bore-profile of a traction motor support-bearing bore in order to optimize alignment with the locomotive axle journal under heavy load conditions, and to thus increase bearing load capacity and bearing life under heavy load conditions.
Proper alignment between the support bearing and the truck axle journal is important for maintaining good bearing performance, because it provides maximum contact between journal and bearing to thus insure minimum unit loading (lbs/sq.in.). This allows the bearing to carry heavier radial loads or the same radial load with greater reliability. This applies to both pinion end (PE) and commutator end (CE) bearings, although it is not as important at the CE position because of the light radial loading at this location.
It is, also, common practice to use the same type of support bearing for both the pinion end and commutator end. Thus, since the greater radial load occurs at the pinion end, such a support bearing must be so designed so as to withstand the greater wear at the pinion end. This current parts-interchangeability requirement of support bearings for use at either pinion end or commutator end, therefore, results in a bearing which is acceptable for either position, but optimum for neither position. Therefore, it is current practice to use identical support bearings at both the heavily loaded PE position and the lesser-loaded CE position for locomotive traction motors equipped with plain friction bearings. Thus, when providing a new type of bore for a support bearing for a locomotive truck axle, ideally one would optimize the bearing bore for the misalignment conditions existing at the PE position, and do this in a way which allows continued use at the CE position, even though not optimized for that lesser-loaded bearing position.
The primary cause of support bearing misalignment is bending due to locomotive weight, and this factor alone theoretically should tend to cause the upper load zone of the support bearing to move an in inboard direction away from the center position of the support-bearing bore, while also causing the lower load zone thereof to move to an outboard location away from the center position of bore. However, in actual use, it has been found that such does not actually occur at the PE; instead, it has been found that upper load zone remains generally centrally-located while the lower load zone does move off-center toward the outboard end of the support bearing. The problem has been to understand why this occurs, and then to develop a bore-contour or profile consistent with the findings as to the additional bending torques present causing the shift of the load zones from the expected, which contour will preserve the existing ideal location of the upper load zone while moving the lower zone into a central position.
In U.S. Pat. No. 4,940,002, which is incorporated by reference herein, there is disclosed a friction support bearing having, in a first version, a skewed or tilted internal bore design, which bore design more accurately positions the truck axle journal therein during heavy load conditions. This prior-art bore design takes into consideration the torque and bending loads of the truck axle arising from the laterally-spaced radial forces emanating from the weight of the locomotive acting on the journal box bearings at the end of the axle and the reactive force of the rail track acting on the wheel mounted by the axle, which bending of the axle directly causes misalignment of the axle portion extending through the traction-motor friction support bearing with the bore of the support bearing. This misalignment causes excessive loading and wear of the support bearing on the pinion-end thereof adjacent the axle's drive gear. However, while this prior-art bore-design may help to alleviate some excessive load concentration on the pinion-end of the support bearing, it has not completely solved the problem. In a second version U.S. Pat. No. 4,940,002, there is disclosed forming the interior bore as variable or changing conical sections, where there are actually four separate conical sections employed. In this second version, there is provided an upper central portion of the bore that is a substantially horizontal line or surface, when viewed in vertical cross section, while the lower or bottom central portion of the bore is somewhat sloped.
The loading of a typical, prior-art traction-motor pinion-end support bearing having a standard cylindrical bore without the improved bore-profile of above-mentioned U.S. Pat. No. 4,940,002, is shown in FIG. 1. For best overall performance and life of a traction-motor support bearing 10, the load zones for loading the truck axle should be centered. This is so in order that the lubricant entering the interior of the bearing via a wick window 12 lubricates all contacting surface-areas, which wick lubricator contacts the axle's journal through the window. In addition, both load zones should be contained within the total axial dimension of the wick if at all possible, again to ensure the best possible lubrication. The example shown in of FIG. 1 is for plain friction support bearings from traction motors with 8″ nominal diameter axles, with approximately 60,000 to 70,000 pounds axle load and standard gauge wheel spacing. This combination of parameters has an axle bending slope of about 0.001 inch/inch at the mid-length portion of the PE bearing. Each PE traction-motor support bearing 10 has two load zones, an upper 14 and a lower 16, and these tend to be heaviest around 25° from vertical because of commonly-used 25° gear-tooth pressure angle. Both load-contact patterns can be seen in the window half of the PE bearing with the upper load pattern above the lubricator access-window and the lower load pattern below the window. The axial location of these contact-patterns is of particular interest, since it is key to understanding the misalignment existing between the axle-journal and the support bearing. It may be seen in FIG. 1 that the upper load contact-pattern is well centered in the bearing length, while the lower load contact-pattern is displaced outwardly, or outboardly toward the bearing flange. Ideally, both upper and lower load contact-patterns should be centered at mid-length of the window, in order that the wick lubricator, which contacts the journal through the window, provides the best possible lubrication. Further, both load contact-patterns should be contained within the total axial dimension or limits of the wick lubricator if at all possible, again to ensure the best possible lubrication. As may be seen in FIG. 1, only the upper load zone is centered.
While used prior-art cylindrical-bore bearings have exhibited an upper load-zone 14 that is centered, such is not the case for the lower load-zone 16, which is skewed toward the outboard end, or bearing flange. Both load zones 14, 16 are actually visible in the window half of a PE bearing, with the upper load zone above the window and the lower load zone below the window. The above-described and shown load-patterns have been observed on General Motor's Electric Motor Division (EMD) traction motors, such as that disclosed in above-mentioned U.S. Pat. No. 4,940,002, with 8″ diameter axles and standard gauge wheel spacing.
Neither version disclosed in above-mentioned U.S. Pat. No. 4,940,002 is effective in solving the misalignment of the lower load zone 16. This is so since the bore-profile of U.S. Pat. No. 4,940,002 only takes into account axle-bending torques associated with locomotive weight. However, according to the present invention, it has been discovered that other loads and torques are present that cause axle-bending and concomitant load-bearing misalignment, which hitherto have not been taken into account into the consideration of a traction-motor support-bearing bore profile.